In general, washing machines are apparatuses for treating laundry by applying physical and chemical actions to the laundry using water and a detergent. A washing machine includes a water reserve tub containing water, a washing tub rotating about a vertical axis in the water reserve tub with laundry therein, and a pulsator rotating in the washing tub and removing dirt from the laundry by a frictional force between the pulsator and the laundry. The pulsator and/or washing tub rotates to remove contaminants from the laundry, the water reserve tub is drained, and thereafter the washing tub spins at high speed to dehydrate the laundry.
An excessive vibration may occur when the washing tub is rotated with laundry which is not evenly distributed. In order to prevent this, the following sequence may be done in conventional washing machines: rotating the pulsator alternately in opposite directions at the last step of the washing cycle to untangle the laundry, draining wash water, rotating the washing tub, sensing an imbalance of the washing tub during the rotation, and if a sensed degree of imbalance is within an allowable range, rotating the washing tub at high speed thereby laundry is dehydrated.
Such way, however, cannot respond to the case where drain is done with the laundry not fully untangled and thus the sensed degree of imbalance goes off the allowable range. Because the twisted or knotted clothes would not be readily redistributed or untangled without wash water in the washing tub despite the spinning of the pulsator or washing tub. A main force exerted to the laundry in washing machines where the washing tub spins about the vertical axis is an inertial force in the direction of gravity, and this force acts in a direction independent from the rotation of the washing tub or pulsator, rendering it difficult for the laundry to change its state without a water flow.
Accordingly, redistributing and imbalance sensing are performed repeatedly until the degree of imbalance reaches an allowable range, which delays entry into the dehydration cycle. In some cases, the degree of imbalance fails to come in the allowable range even with repetitive redistributing, leaving the cycle to stay before dehydration while coming up with an error. Therefore, the user needs to remove the cause of the imbalance on his own.